Can you give a few details as when you add the lye,quantity etc.How do you test for ph?.I can see me having to pay for wvo in the near future so alternatives is something i am interested in.Since i am setting up heaters for veg on the exhaust and injector line i might as well use them for wmo as well.
I start by mixing some diesel fuel with the oil to thin it. I heat it and run it through a Dieselcraft centrifuge filter. I use 3 gal diesel to 7 gal of wmo for a batch. That lets it start filtering with the Dieselcraft while it is warming up. Saves a little time.
Testing
I mix 50/50 wmo and distilled water in a clean dish soap container, shake well and stand upside down till the water settles out, about 10 to 20 minutes. I then gently move the soap container over a bowl and quickly open and close the container allowing a few drops of water to fall into the bowl. I then check it with litmus paper. I get litmus paper on the net for about $1 a hundred and tear them in half.
NOTE: “LYE IS VERY DANGEROUS”, it will dissolve your skin and blind you permanently. Wear full face protection, rubber gloves, long sleeves, suit of armor etc.
To add lye I SLOWLY add it to distilled water in a glass jar setting in a pan of water so the glass does not break from the heat. As it cools I add a little more. I have never tried to see how much you can add until it will not dissolve any more, I eventually cringe at how much is in there before that happens. Be VERY afraid of lye.
While the WMO is being pumped through the Dieselcraft filter I add a little lye/water at a time and let it recirculate for about 20 minutes and check it again. By heating the oil the water will eventually evaporate the water leaving the lye in the oil to counter the acidity. Keep checking and adding a little at a time until you come up neutral on the litmus paper.
I usualy put an add in the local freectcle.com when I need waste motor oil. I usualy get around 200 gallons at a time. I also have some people pay me a dollar a gallon to bring it to me. You have to take it for free on freecycle though.